Turbine disc and blade mounting



July 1, 1958 J. T. PURVIS ETAL TURBINE DISC AND BLADE MOUNTING 2 Sheets-Sheet 1 Filed Sept. 17, 1953 July 1, 1958 J. T. PURVIS ET AL 2,841,363

TURBINE DISC AND BLADE MOUNTING Filed Sept. 17, 1953 2 Sheets-Sheet 2 II [6, lb

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m'rorqglevs United States Patent fiic 2,841,363 ?atented July 1, 1958 rUamNE Disc AND BLADE MoUNTiNG Joseph Thompson Purvis, Etobicohe Township, (intario, and Robert Wlitcheil Sachs, North York Township, Ontario, Canada, assignors to A. V. Roe Canada, Limited, Peel, Ontario, Canada, a corporation Application September 17, 1953, Serial No. 380,834

7 Claims. (Cl. 253-77) This invention relates to the rotors of rotary power conversion machines and particularly to those comprising discs having radially disposed open slits angularly spaced around their rims.

In such machines the high temperature working fluid passing through the blading causes the blades and the rim of the disc upon which the blades are mounted to become very hot, whereas the other portions of the disc are usually cooled by some means to preserve the physical properties of the material and to prevent the conduction of heat to the rotor bearings. The resulting temperature differential between the rim and the other portions of the disc, together withthe high centrifugal loading to which the disc is subjected under operating conditions, introduces severe internal stresses and these may cause some yield in the material, which in turn will induce other internal stresses when the rotor is stopped and allowed to cool.

Repeated heating and cooling may cause cracking and it has therefore been the custom to provide ample material to absorb thermal and centrifugal stresses, with the result that the discs have been unduly heavy and structurally ineflicient.

To overcome the aforementioned difficulty, radially disposed open slits have been angularly spaced around the rims of such discs, to permit some degree of circumferential expansion and contraction without subjecting the rims tohoop stresses.

However, since there is usually a considerable pressure gradient in the working fluid across a stage, there is a tendency for the hot working fluid to leak through the slits, thus heating and reducing the strength of the rim and the mounting of the blades therein.

It is customary to mount the blades in the rim of a rotor by the provision of dove-tail or fir-tree roots on the blades, which slide, substantially axially of the rotor, into corresponding slots circumferentially spaced around the periphery of the rotor disc. 'It is, of course, necessary to provide some means of locking each blade against axial movement to retain it in its slot after it has been inserted. This may be achieved by the provision of some dowel or pin, engaging a recess in the blade root transversely of the direction in which the blade is otherwise free to slide in the slot.

It is an object of this invention to provide dowels or pins peculiarly adapted to lock the blades in a rotor disc of the type having radial slits around the rim to accommodate expansion and contraction thereof, and to arrange the said dowels or pins so that they effectively prevent any leakage of the working fluid through the said slits. Other dbjects and advantages of the invention will be apparent from the following description of a preferred application thereof,

In the accompanying drawings, forming a part of this application and in which each reference character denotes the same part in all the views:

Fig. 1 is a side elevational view of a gas turbine jet engine incorporating the invention, partly, cut away to show a portion of the turbine rotor disc and blades,

Fig. 2 is a fragmentary front elevational view of an arrangement of the turbine rotor blades on the rim of the turbine disc according to the invention,

Fig. 3 is an axial section 'of the turbine disc and a blade on the line 3-3 of Fig. 2,

Fig. 4 is an enlarged perspective view of the sealing pin shown in Fig. 3,

Fig. 5 is an enlarged perspective view of a portion of Fig. 3 showing a manner of securing the pin in position after assembly in the rotor, and

Fig. 6 is a view, similar to that of Fig. 3 showing an alternative application of the invention.

In a gas turbine engine such as that shown in Fig. 1 air is drawn into an inlet 10 by an axial flow compressor 11 and discharged at high pressure from the compressor into a combustion system 12. The combustion system comprises a plurality of chambers into which 'fuel is introduced and burned in the aforesaid compressed air, so that the air is discharged at high velocity and high temperature into the turbine 13. The turbine provides the power to drive the compressor ll, through the shaft 14, the exhaust from the turbine being discharged through the tail cone 15 to provide a propulsive thrust.

The turbine 13 comprises a rotor disc 16, carrying on its peripheral rim 17 a plurality of radially disposed blades l8. Means not shown are provided for directing a stream of cooling air upon each side of the rotor disc.

As shown in Figs. 2 and 3 each blade 18 is secured in the rim '17 of the disc 16 by a fir-tree root 19 which engages a corresponding slot 17a disposed in the rim axially with respect to the engine. Although the engagement of the root in the slot obviously prevents any radial movement of the blade, the root is free to slide axially along the slot, its movement in one direction being limited by a tang 20, extending radially from the root and engaging a lateral face 21 of the rim 17.

From the bottom of each slot 17:; in the disc a radially and axially disposed open slit 22 extending from face to face of the disc and rim extends for a short distance towards the centre or hub of the disc. It terminates in a cylindrical hole 23 of slightly greater diameter than the circumferential width of the slit, that is, the width of the slit in a circumferential direction of the rotor. The axis of the hole 23 is parallel to the axis of the disc. To avoid undue weakening of the rotor disc the holes are arranged at alternately greater and lesser radial distances from the centre of the rotor as shown in Fig. 2.

Each slit 22 intersects longitudinally a cylindrical bore or way 24, which may be of the same diameter as the The blade is positively located within the slot by a tubular pin 26 formed of a Wall of resilient elastic material such as lconel, curved in cross-section as, for in- V the terminal portion from 3 stance,--to form a generally cylindrical hollow shell as shownin Fig. 4 and disposed in the bore 24.

A tubular pin 26 preferably has a slot 26a along its full length (see Fig. 4), rendering it more resilienfly yieldable across its width or diameter. transverse slot 27 adjacent one end also. The head portion 26b of the pin 26 between the slot 27 and the end 26c adjacent thereto, is accommodated in the recess 25, and

p the adjacent end 26c or" the pin bears against the side of therecess remote from the tang and holds the .tang firmly against the face 21.

The outside diameter of the pin is slightly larger than the-diameter ,of the oblique bore 24, necessitating some radial compression of the pin as it is inserted into the radially inner end thereof. However, as the head portion 26I7Yemerges from thebore into the recess it is progressively relieved of this cotnpression until, when the transverse slot 27 emerges from the bore, the head portion of :he'pin is free to expand to itsnatural shape. This expension e'fiectively prevents-the pin from. being with drawn from the bore or from inadvertently falling out. To remove the blade from the disc it is necessary to shear the pin,- by forcibly driving the blade root from the slot. Because the pin is under radial compression in the hole andtraverses the entire radial length of the slit 22, it efiectively seals the slitagainst any leakage of Working fluid from one side of the disc to 'the }o ther. On the other hand, since the pin is itself slottedit exerts no material restrain upon any expansion,

or contraction of the rim 17. Thus it will be understood that the pin serves the dual purpose of providing a positive lock of the blade root in its slot, acting in this respect in conjunction with the tang, and of sealing the slit in the 'disc against leakage.

' In the alternative construction shown in Fig. 6 the turbinerotor comprises two substantially parallel discs 16' and 16 enclosing betweentheir rims 17 and 17'. anannular groove 17a of fir-ti ee form in axial crosssection. In .this construction the root 19 of each blade 18 is disposed circumferentially of the rotor and is accornmodated in the aforesaid annular groove 17a. As in the previously described construction a radially and Ithas a short axially disposed open, slit 22 is provided extending I through ,both rotor discs substantially on the longitudinal axis of each blade 18', to permit circumferential expansionfand'contraction of the rims 17. and '17" of the discs.

Each slit terminates in a cylindrical hole 23' or 23" as the case mayjbe, of slightly greater diameter than the circumferential width of the'slotand disposed with its axis'parallel to the axis of the discs, and a cylindrical bore 24' of the same diameter as the hole 23' and lying entirelywithin disc 16', extends obliquely from one end of the hole 23'; to a location, in the space defined by the said annular groove 17a which is in alignment with a recess 25 'inthe blade root, when the blade is assembled in the rotor. I

'The blade is secured radially by virtue of the fir-tree configurationofits root in the annular groove defined by rims-17 and 17", andcircumferentially by a pin 26, similar inevery respect to the pin 26 of the previously described construction, which is driven through the obliquely disposed bore 24' into the recess 25'. It will be apparent that this pin 26 also serves to seal the slits 22' and 22'f againstany leakage of working fluid from one side to the other of the particular rotor disc in which the pin is fitted,'but sinceit is customary to arrange .such discs-.16 and 16" with a space 28 between them, at least one of the discs must carry pins 26f in every slit 22 in order to provide a complete seal across the assembly.

The forms of the invention herein shown and described are. to be taken as preferred examples and variinward from its circumference,---and havinga blade -slot in its circumference adjacent the slit, a blade slidable in the blade slot, the slot having an axis along which the blade slides, a locking member disposed in the slit at an angle to the said axis and having one end projecting outward into the blade slot, the said end of the locking members engaging the blade and preventing sliding movement of the blade in the blade slot, and means retaining the blade in the blade slot. 7

2. Ina rotary power'convers'ion machine, a rotor disc having a substantially radially disposed slit extending for the full thickness of the disc inward from its circumference to accommodate circumferential expansion and coning movement of the bladeinthe :blade slot, and means retaining the blade in theblade. slot.

3. In a rotary power conversion machine 'arotordisc, 3

having a substantially radially; disposed. openslitextend:

blade slot in its which the blade slides,

radial length of the slit,.-the .pin,sealingly fitting,andclosing the slit against the 'pass age of working lluii the pin being arranged at an angle to the,,d irectionpf sliding of the blade and having onev end projectingoutwardinto the blade slot, the said end of the pinengaging thehladeand; preventing sliding movement of the blade in the blade,

slot, and means retainingthe bladejn the blade slot 4. In a rotary power. conversion,machine,-;a rotor disc having a substantially radially disposed open sht xtfindr ing forv the full thickness of the disc inwar cumference to accommodate circumferen and contraction of the discin operation a I blade slot in its circumference in radial;regit;ra

the slit, a bladeslidable in the blade slot,;the slothaving of 1:

an axis along whichv the'blade slides,;. a .p not less than the circumferential width of tending for the full radial lengthof the -s lit,;t-he pin;

said axis one end of the pin projecting :outward into the blade slot andengaging; the blade;;to prevent; sliding; I movement of vthe blade in thebladeslot, andmeans re: 1

taining the. blade inthe blade ;slot.

5. In a rotary power conversionmachine, a rotorzldisc having a substantially; radially disposed ,opemslit' having parallel facing walls and extending forthefull thickness the slit so as to providea borehavinga .width circumferentially of the ;disc greaterithan.thescorrespondingi-n, Width of theslit, and a blade. slot .in the-circumference of the rotor disc in radial registrationwiththe bore, .a blade slidable in the -.blade.slot, the.-slothaving amaxis along which the blade slide's a 'piniinthetborezand extending atan angle to the said axisandhaving one end projecting outward into thebla'deIslot, the said end-of the pin engaging the blade and preventing..sliding,move--.-=

. b ing formed of a wall of resilient; material curved-in oross;sec,-;.; tion and resiliently yieldable. across itswidth nd seal- .7. ingly fittingand closing the slit against the passage of; working fluid, the pin. being arranged at anangleto the 5 ment-of the blade in the blade slot, and means retaining the blade in the blade slot.

6. In a rotary power conversion machine, the combination claimed in claim 5 in which the pin is formed by a wall of resilient material curved in cross-section and normally of outside diameter greater than the diameter of the bore, the wall of the pin having 2. Iongitudinal slot for its full length.

7. In a rotary power conversion machine, the combination claimed in claim 6 including means for securing the pin in place that comprise a recess in the blade root for loosely receiving the projecting end of the pin, and a transverse slot in the wall of the pin intersecting the longitudinal slot and freeing a portion of the wall of the projecting end of the pin for expansion in the recess in the blade root beyond the diameter of the bore.

References Cited in the tile of this patent UNITED STATES PATENTS 1,619,133 Kasley Mar. 1, 1927 2,434,935 Kroon Ian. 27, 1948 2,657,008 Atkinson Oct. 27, 1953 FOREIGN PATENTS 131,574 Australia Mar. 1, 1949 241,993 Switzerland Sept. 2, 1946 312,864 Italy Nov. 28, 1933 609,446 Great Britain Sept. 30, 1948 

